Method and apparatus for vasculature visualization with applications in neurosurgery and neurology

ABSTRACT

The invention provides methods and systems for neurovascular imaging ( 150 ).

FIELD OF THE INVENTION

The invention relates generally to the field of medical imaging. Certainembodiments of the invention provide methods for imaging vasculature ina subject. Certain other embodiments provide systems which are usefulfor imaging vasculature in a subject.

BACKGROUND OF THE INVENTION

Imaging of biological tissues and organs assists doctors in bothdiagnosis and treatment. A variety of medical techniques which aresuitable for imaging biological tissues and organs are known. Theseinclude traditional x-rays, ultra-sound, as well as magnetic resonanceimaging (MRI), and computerized tomography (CT). A variety of dyes usedin medical imaging have also been described including radio opaque dyes,fluorescent, as well, as colorimetric dyes (see e.g., U.S. Pat. Nos.5,699,798; 5,279,298; 6,351,663; and U.S. patent application Ser. No.10/365,028). Imaging techniques and systems using fluorescent dyes havebeen described for the heart and eye (see, U.S. Pat. Nos. 5,279,298 and6,915,154; and U.S. patent application Ser. No. 10/619,548, all of whichare incorporated by reference in their entirety). Some dyes can serveboth an imaging function, as well as a therapeutic function (see, e.g.U.S. Pat. No. 6,840,933). It would be useful to provide imaging methodsand systems that could be used to view vasculature maladies associatedwith the central nervous system and/or brain.

One example of a malady affecting the brain is cerebral arteriovenousmalformation (AVM). AVM is a disorder of the blood vessels in the brain,in which there is an abnormal connection between the arteries and theveins. Thus, a connection between arteries and veins occurs withouthaving the normal capillary bed between them. Arteriovenousmalformations vary in their size and location within the brain. It is acongenital disorder. The AVM consists of blood vessels termed “nidus”(nest) through which arteries connect directly to veins, instead ofthrough the elaborate collection of capillaries. Over time, the AVMtends to enlarge as the great pressure of the arterial vessels can notbe handled by the veins that drain out of it. This causes a largecollection of worm-like vessels to develop (malform) into a mass capableof bleeding at some future time. These malformations are most likely tobleed between the ages of 10-55.

There are often no symptoms until complications occur, which involverupture of the AVM and a resulting sudden bleed in the brain i.e. ahemorrhagic stroke. When symptoms do occur before an AVM ruptures, theyare related to smaller and slower bleeding from the abnormal vessels,which are often fragile because their structure is abnormal.

In more than half of patients with AVM, hemorrhage from the malformationis the first symptom. Depending on the location and the severity of thebleed, the hemorrhage can be profoundly disabling or fatal. The risk ofbleeding from an AVM is approximately 2-4% per year. Cerebralarteriovenous malformations occur in approximately 3 out of 10,000people. If an AVM bleeds once, the risk is greater that it will bleedagain in the future. Intracerebral or subarachnoid hemorrhages are themost common first symptoms of cerebral arteriovenous malformation (see,e.g., Ojemann R G, Ogilvy C S, Heros R C, Crowell R M, eds. SurgicalManagement of Cerebrovascular Disease, Third edition, 2005, Williams &Wilkins, Baltimore).

The first symptoms often include headache, seizure, or other suddenneurological problems, such as vision problems, weakness, inability tomove a limb or a side of the body, lack of sensation in part of thebody, or abnormal sensations.

Open brain surgery, endovascular treatment, and radiosurgery are some ofthe treatments used. Often these treatment options will be used incombination. Very large AVMs may short-circuit blood flow enough tocause cardiac decompensation in which the heart is unable to pump enoughblood to compensate for bleeding in the brain. This condition is usuallyidentified in infants and young children.

Surgery is dependent upon the accessibility and size of the lesion andthe status of the patient at the time of surgery. Open brain surgery isthe actual removal of the malformation in the brain through an openingmade in the skull.

Systems and methods which provide for imaging vasculature associatedwith AVM would assist the surgeon in locating the AVM and thus would aidin achieving a successful outcome to the procedure. Similarly, the samemethods and systems could be used to confirm that the AVM has beenremoved.

Traditional imaging methods used in the context of AVM, such asmeasuring arterial pulsation or angiography using digital subtractionare either unreliable or expensive and inconvenient to be used duringsurgery (see, e.g., Wrobel et al., 1994, Neurosurgery 35(5):970; Martinet al., 1990, J. Neurosurg. 73:526). A need therefore exists forimproved imaging methods and systems which provide for the rapid,accurate and inexpensive imaging of maladies affecting the vasculatureassociated with the brain and central nervous system, e.g., AVM.

SUMMARY OF THE INVENTION

In certain embodiments, the invention provides a method ofintra-operatively confirming the removal of at least one vesselcomprising an arteriovenous malformation in a subject. The methodincludes the steps of (a) administering a fluorescent dye to therecipient subject; (b) applying a sufficient amount of energy to thevessel such that the fluorescent dye fluoresces; (c) obtaining afluorescent image of the vessel; and (d) observing the image todetermine if a fluorescent signal stops at a point of removal of thevessel, wherein a lack of a fluorescent signal downstream of the pointof removal indicates the arteriovenous malformation has been removed.

In certain embodiments, the invention provides a method ofintra-operatively locating at least one vessel comprising anarteriovenous malformation in a subject. The method includes the stepsof (a) administering a fluorescent dye to the recipient subject; (b)applying a sufficient amount of energy to the vessel such that thefluorescent dye fluoresces; (c) obtaining a fluorescent image of thevessel; and (d) observing the image to determine if the fluorescentsignal leaks from a vessel suspected of comprising an arteriovenousmalformation, wherein a leak of a fluorescent signal from a vesselsuspected of comprising an arteriovenous malformation indicates thepresence of an arteriovenous malformation.

In some embodiments, the invention provides a portable system useful forimaging at least one vessel comprising an arteriovenous malformationcomprising a fluorescent dye in a subject comprising (a) an energysource capable of emitting sufficient energy such that the fluorescentdye fluoresces; and (b) an imaging head.

An imaging method is further provided in certain embodiments thatincludes the steps of: (a) administering a fluorescent dye to therecipient subject; (b) applying a sufficient amount of energy to thevessel such that the fluorescent dye fluoresces; (c) obtaining afluorescent image of the vessel; and (d) determining the presence orabsence of an occlusion or stenosis, wherein jagged edges, or a changein thickness indicates a stenosis and a discontinuous signal indicatesan occlusion.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings in which:

FIG. 1 is a schematic diagram showing one embodiment of the system ofthe invention. FIG. 1 shows an example of an electrical configuration.

FIG. 2 illustrates imaging software that may be used in certainembodiments of the invention.

FIG. 3 illustrates an embodiment of the invention

DETAILED DESCRIPTION

Hereinafter, aspects in accordance with various embodiments of theinvention will be described. As used herein, any term in the singularmay be interpreted to be in the plural, and alternatively, any term inthe plural may be interpreted to be in the singular.

DEFINITIONS

“Approximately”, “substantially” and “about” each mean within 10%,preferably within 6%, more preferably within 4% even more preferablywithin 2%, and most preferably within 0.5%.

“Computer” as used herein, refers to a conventional computer asunderstood by the skilled artisan. For example, a computer generallyincludes a central processing unit that may be implemented with aconventional microprocessor, a random access memory (RAM) for temporarystorage of information, and a read only memory (ROM) for permanentstorage of information. A memory controller is provided for controllingRAM. A bus interconnects the components of the computer system. A buscontroller is provided for controlling the bus. An interrupt controlleris used for receiving and processing various interrupt signals from thesystem components. Mass storage may be provided by diskette, CD ROM orhard drive. Data and software may be exchanged with computer system viaremovable media such as the diskette or CD ROM. A CD ROM drive isconnected to the bus by the controller. The hard disk is part of a fixeddisk drive that is connected to the bus by a controller. User input tothe computer may be provided by a number of devices. For example, akeyboard and mouse may be connected to the bus by a controller. An audiotransducer that might act as both a microphone and a speaker may beconnected to the bus by an audio controller. It will be obvious to thosereasonably skilled in the art that other input devices, such as a penand/or tablet may be connected to the bus and an appropriate controllerand software, as required. A visual display can be generated by a videocontroller that controls a video display. Preferably, the computerfurther includes a network interface that allows the system to beinterconnected to a local area network (LAN) or a wide area network(WAN). Operation of the computer is generally controlled and coordinatedby operating system software, such as the Solaris operating system,commercially available from Sun Microsystems, the UNIX® operatingsystem, commercially available from The Open Group, Cambridge, Mass.,the OS/2® operating system, commercially available from InternationalBusiness Machines Corporation, Boca Raton, Fla., or the Windows NToperating system, commercially available from MicroSoft Corp., Redmond,Wash. The operating system controls allocation of system resources andperforms tasks such as processing scheduling, memory management,networking, and I/O services, among things. In particular, an operatingsystem resident in system memory and running on the CPU coordinates theoperation of the other elements of computer.

As used herein, “wavelength of interest” refers to light in both thevisible and infra red spectrum. In another embodiment, it refers tolight in only the infra red spectrum. In yet another embodiment, itincludes light at the wavelength at which ICG fluoresces. In yet anotherembodiment, it includes light between about 825 and about 835 nm. In yetanother embodiment, it includes light wavelength(s) at which one or moreother fluorescent dyes emit energy when excited. The invention providessystems and methods for imaging neurovasculature, e.g., the vasculatureassociated with AVM or an aneurysm. The neurovasculature of interest maybe associated with the central nervous system (e.g., brain, or spine) orthe peripheral nervous system (e.g., in a limb). Surgical removal ofAVMs is not without serious risk. In certain embodiments the instantinvention seeks to minimize the risks associated with surgery to removeAVMs by providing imaging systems and methods which permit the surgeonto intra-operatively locate the position of the AVM, and thus preventdamaging or cutting vasculature not associated with AVM and hencedecrease the chance of stroke and other iatrogenesis. In otherembodiments the systems and methods of the invention may also be used toconfirm that the AVM has been successfully removed.

Methods of the Invention

In certain embodiments the invention provides a method for imaging atleast one vessel, in a subject, wherein the vessel is associated with anAVM. The vessel may include an artery or a vein or a nidus associatedwith an AVM. Associated refers to vessels which either feed or drain theAVM or are vessels which comprise the AVM. The image may be obtainedintra-operatively. Thus the vessel may be surgically exposed.

The method comprises administering a fluorescent dye to the subject.Exposing the vessel to a form of radiant energy such that thefluorescent dye fluoresces and obtaining an image of at least one vesselassociated with the AVM. By observing the fluorescent image the surgeoncan locate the AVM in the subject. Blood flow through the AVM may appeardifferent. As an example, but not as a limitation, the vessel may appearto have small leaks in it due to the weakened structure of the vesselscomprising the AVM. In this case the fluorescent dye would leak into theextra-vascular tissue. In addition, once the AVM has been removed thesurgeon can confirm that there are no remaining leaky vessels and thatthe surgically cut vessels have been sealed properly.

The invention also contemplates obtaining a plurality of images. Theplurality of images may be compared to each other to determine theeffectiveness of a therapy, e.g. an administered pharmaceuticalcompound, a surgical procedure.

In yet another embodiment, the invention provides a method for imagingto determine the absence, presence or perfusion of tumors. The methodincludes the steps of (a) selecting a portion of body tissue to beimaged, (b) obtaining at least one angiographic image of that bodytissue, (c) and examining the at least one angiographic image to assessthe extent of blood flow within the selected body tissue. Since tumorsare often inappropriately perfused, the physician may be able todetermine not only the presence or absence of a tumor, but also its sizeand margins. The information can be used to not only locate tumors butto also later confirm that a procedure to remove the tumor has beensuccessful. In such embodiments, the tissue of interest will be imagedbefore the tumor-removal procedure to locate or confirm the position ofa tumor and also after the procedure to confirm the tumor has beensuccessfully removed.

In certain embodiments the invention provides a method of determiningthe patency of a vessel comprising a lumen. In some embodiments patencymay be determined by visually inspecting an image of the vessel. As anexample, but not as a limitation, a continuous signal from a dye that isuniform in thickness may indicate patency. As another non-limitingexample an image displaying jagged edges, or a change in thickness mayindicate stenosis. Similarly a discontinuous signal may indicateocclusion.

Subject as used herein, refers to any animal. The animal may be amammal. Examples of suitable mammals include, but are not limited to,humans, non-human primates, dogs, cats, sheep, cows, pigs, horses, mice,rats, rabbits, and guinea pigs.

Dyes

Suitable fluorescent dyes include any non-toxic dye which fluoresceswhen exposed to radiant energy, e.g. light. In certain embodiments thedye is a fluorescent dye that emits light in the infra red spectrum. Incertain embodiments the dye is a tricarbocyanine dye such as indocyaninegreen (ICG). In other embodiments the dye is selected from fluoresceinisothiocyanate, rhodamine, phycoerythrin, phycocyanin, allophycocyanin,o-phthaldehyde, fluorescamine, Rose Bengal, trypan blue, andfluoro-gold. The aforementioned dyes may be mixed or combined in certainembodiments. In some embodiments dye analogs may be used. A dye analogincludes a dye that has been chemically modified, but still retains itsability to fluoresce when exposed to radiant energy of an appropriatewavelength.

In some embodiments the dye may be administered intravenously, e.g., asa bolus injection. In some embodiments the bolus injection may comprisea volume of about 0.5 ml. In other embodiments the bolus injection maycomprise a volume in the range of about 0.1 ml to about 10 ml. In someembodiments the dye may be administered parenterally. Where multipledyes are used they may be administered simultaneously, e.g. in a singlebolus, or sequentially, e.g. in separate boluses. In some embodimentsthe dye may be administered by a catheter or cannula, e.g. during aminimally invasive procedure.

The dye may be administered at a suitable concentration such that thefluorescence may be detected when the appropriate wavelength of radiantenergy is applied. In some embodiments where the dye is ICG a suitableconcentration is about 0.03 mg/ml at the site of detection. In otherembodiments a suitable concentration of ICG is in the range of about0.003 mg/ml to about 75 mg/ml. In some embodiments the ICG isadministered in the range of about 1 mg/kg body weight to about 6 mg/kgbody weight. In yet other embodiments the dye is administered at aconcentration of about 0.5 mg/kg body weight. In still other embodimentsthe dye is administered in a range of about 0.01 mg/kg body weight toabout 3 mg/kg body weight. In certain embodiments a suitable maximumdaily dose of ICG may be administered to a subject. The maximum dailydose may be in the range of about 70 mg-about 140 mg.

The dye may be provided as a lyophilized powder or solid. In certainembodiments it may be provided in a vial, e.g. a sterile vial which maypermit reconstitution with a sterile syringe. It may be reconstitutedusing any appropriate carrier or diluent. Examples of carriers anddiluents are provided below. In certain embodiments the dye may bereconstituted at a concentration in the range of about 0.001 mg/ml-100mg/ml. In other embodiments the dye is reconstituted to a concentrationof about 10 mg/ml, about 20 mg/ml, about 30 mg/ml, about 40 mg/ml, about50 mg/ml. The dye may be reconstituted, e.g., with water, immediatelybefore administration.

In certain embodiments the dye may be administered to the subject lessthan an hour in advance of obtaining an image. In some embodiments thedye may be administered to the subject less than 30 minutes in advanceof obtaining an image. In yet other embodiments the dye may beadministered at least 30 seconds in advance of obtaining an image. Instill other embodiments the dye is administered contemporaneously withobtaining an image.

Diluents and Carriers

Any diluent or carrier which will maintain the dye in solution may beused. As an example, in certain embodiments where the dye is ICG the dyemay be reconstituted with water. In other embodiments where the dye isICG, the dye may be reconstituted with an alcohol, e.g. ethyl alcohol.In some embodiments once the dye is reconstituted it may be mixed withadditional diluents and carriers. In some embodiments the dye may beconjugated to another molecule, e.g., a protein, a peptide, an aminoacid, a synthetic polymer, or a sugar, e.g., to enhance solubility or toenhance stability.

Additional examples of diluents and carriers which may be used in theinvention include glycerin, polyethylene glycol, propylene glycol,polysorbate 80, Tweens, liposomes, amino acids, lecithin, dodecylsulfate, phospholipids, deoxycholate, soybean oil, vegetable oil,safflower oil, sesame oil, peanut oil, cottonseed oil, sorbitol, acacia,aluminum monostearate, polyoxylethylated fatty acids, and mixturesthereof. Additional buffering agents may optionally be added includingTris, HCl, NaOH, phosphate buffer, HEPES.

Radiant Energy

In certain embodiments of the invention radiant energy is applied to thevessels in the region suspected of having an AVM or otherneurovasculature of interest in an amount sufficient to cause afluorescent dye to fluoresce thereby permitting at least one vesselassociated with the AVM to be imaged. In some embodiments the energy islight energy. In some embodiments the source of the light energy is alaser. An example of a suitable laser is the Magnum 3000 (LasirisSt-Laurent, Quebec, Canada), however, the skilled artisan willappreciate many other suitable lasers are commercially available. Thelaser may be comprised of a driver and diode. Preferably, the laser is ahigh power laser diodes (HPLDs). Examples of HPLDs include AlInGaAsPlasers and GaAs lasers which are well known in the art. Such sources canbe single diodes (single emitters), or diode-laser bars, which are madefrom edge emitting semiconductor chips. The laser may optionally includea filter, e.g. a bandpass filter, to ensure that the emitted radiationis of a substantially uniform wavelength. The laser may comprise opticsfor diverging the laser. The optics may be adjustable permittingvariation in the field of illumination. The adjustable optics may alsobe used to provide even illumination over a given area.

In some embodiments the laser output is continuous or quasi continuous.In other embodiments the laser output is pulsed. The pulsed output maybe synchronized with image acquisition by using a pulse generator. Insome embodiments the laser pulse may last for at least 3 femtoseconds.In some embodiments the laser output lasts for about 30 seconds. Inother embodiments the laser output lasts about 0.5 seconds-about 60seconds. A suitable repetition rate for the pulsed laser may be in therange of e.g., 1 Hz-80 MHz, 10 Hz-100 Hz, 100 Hz-1 kHz, 1 kHz-100 kHz,100 kHz-80 MHz. In some embodiments the laser may be operated at poweroutput of 2.2 watts. In other embodiments the laser may be operated atpower output in the range of 1-4 watts. In still other embodiments theaverage power is less than 5 watts.

In some embodiments the source of the light energy is an incandescentlight with an appropriate filter so as to provide a suitable wavelengthof light to induce the fluorescent dye to fluoresce. In yet otherembodiments the light source is light emitting diode (LED). In someembodiments the light energy may have a wavelength in the range of 150nm-1500 nm. In other embodiments the light energy may be comprised ofinfra red light. In some embodiments the administered light has awavelength of about 805 nm. In other embodiments the administered lighthas a wavelength in the range of about 805 nm-850 nm. The light energymay be administered at a wavelength which is shorter than the collectionwavelength, i.e. detection wavelength. The light energy may beadministered diffusely so as not to damage the irradiated tissue. Insome embodiments the light is administered over an area of about 1inch×1 inch. In another embodiment, the field of view is between about0.5 inches to about 2 inches in one dimension, and between about 0.5inches to about 2 inches in a second dimension. In yet anotherembodiment, the first and second dimensions are both between about 0.5inches and about 1.5 inches. In some embodiments, the field of viewranges from about 1 cm to about 20 cm in each dimension. Preferably, thefield of illumination is about equal to the field of view. Theirradiance is in the range of about 15-25 mW/cm², and in someembodiments between about 18-22 mW/cm². Appropriate fields of view andillumination and irradiance levels can be achieved by modifyingprojection optics that are in optical communication with a laser lightguide, as is well known to the skilled artisan. As described above,multiple dyes may be used in some embodiments. In these embodiments,multiple light sources may be used, e.g., a first laser to excite afirst dye and a second laser to excite the second dye. The skilledartisan will understand that the light source will be chosen orconfigured to excite a particular dye. In another embodiment, a singlelight source may be configured to excite multiple dyes, e.g., byalternating the wavelength at which energy is emitted.

Image Acquisition

Image acquisition may be achieved using any sensor capable of detectinga fluorescent signal. Examples include silicon based sensors, compositemetal oxide semi oxide (CMOS) sensors and photographic film. In oneembodiment the sensor comprises a camera, e.g. charge coupled device(CCD). Examples of a CCD include the Hitachi KP-M2; KP-M3 (Hitachi,Tokyo, Japan).

In certain embodiments an endoscope may be used, e.g., for aninterventional application. It may include a sensor. The endoscope mayadditionally comprise a source of radiant energy. The endoscope may becomprised of optical fibers. In certain other embodiments a microscopecomprising a sensor may be used, e.g., a surgical microscope. In anotherembodiment the sensor comprises a video camera.

In certain embodiments the sensor may capture images at the rate of atleast 10 per second, at least 15 per second, at least 20 per second, atleast 30 per second, or at least 50 per second. Thus in certainembodiments the invention contemplates a plurality of images. In otherembodiments the invention contemplates one image.

The camera may be comprised of a means for focusing the image. Incertain embodiments the invention contemplates a manual means forfocusing an image. In other embodiments the invention contemplates anautomated means for focusing an image. The camera may further becomprised of a lens system that permits magnification of an image field.

In one embodiment the relative positioning of the camera and laser isfixed so as to enhance clarity and minimize background noise. In thisembodiment the laser is located at an angle of less than about 85° withrespect to the axes of the laser and the camera. In another embodimentthe laser is located at an angle from about 20° to about 70° withrespect to the axes of the laser and the camera.

In certain embodiments the camera relays the captured image to an analogto digital converter and then through image capture and processingsoftware running on a computer. The digital image of the fluorescingagent, corresponding to the AVM or other neurovasculature of interestmay then be displayed on a monitor and recorded by the computer or aperipheral device. The image may be stored in any suitable medium, e.g.,a hard drive, an optical disk, magnetic tape. The camera may also directimages to a television/VCR system such that the images may be displayedin real time, recorded and played back at a later time.

Systems of the Invention

The invention provides a system for imaging at least one vesselassociated with an AVM or other neurovasculature of interest, see, e.g.,FIG. 1. The system may be used intra-operatively during surgery on anAVM to visualize at least one surgically exposed vessel associated withthe AVM.

System Overview

FIG. 1 illustrates an example of an electrical configuration of a systemof the invention. In one embodiment, power supply 110 provides energy tothermoelectric cooler and controller 120, energy source 130 andcontroller/timing circuit 140. The controller 120 controls thetemperature of energy source 130. For example, the temperature of adiode laser affects its operating wavelength, (e.g., a 0.3 nm shift perdegree Celsius). In some embodiments, as described below, the energysource 130 may not be a diode laser, and hence a controller 120 may notbe necessary. Controller/timing circuit 140 times the energy source 130to the detector/camera 100 through computer 150. System computer 150receives instructions from computer 150. It also includes imageprocessing software on computer 150 readable medium. Computer 150 is inelectrical communication with camera 100 and display 160. Display 160receives image data from computer 150 and displays it. As describedabove, in some embodiments, the energy source 130 is a laser. It has afiber 170 through which light energy is transmitted. Fiber 170 connectsto illumination lens 180 through which light is illuminated whenmechanical shutter 190 is open. An emission filter 210 may be used tofilter light above or below the wavelengths at which the fluorescent dyeis excited. In other embodiments, the energy source 130 may be an LED.It would directly illuminate the tissue of interest (i.e., no fiber 170may be required.) The light energy irradiates a tissue of interest.Camera 100 captures radiation emitted by the dye after it is excited andtransmits detected data to computer 150. The lens 180, fiber 170, andcamera 100 are part of imaging head 230. The head 230 may be anarticulating head. In some embodiments, head 230 further includes adistance sensor/focus indicator 220. The components of the systems ofthe invention are further described herein.

In certain embodiments, the system comprises: a) an energy source 130capable of emitting sufficient energy such that the fluorescent dyefluoresces; and b) an imaging head 230. The system is configured for usewith the methods disclosed herein. In some embodiments, the systemfurther includes c) an articulating arm; d) a computer 150 and monitor;e) image processing software; f) an electrical power source; and

g) a housing for containing a-f, wherein the housing is portable andcomprises at least 2 wheels. The wheels may have locks to preventunwanted movement. In some embodiments the system may also comprise atleast one of the following: a motion sensor; a distance sensor 220; asterile drape; and a printer. The system may further comprise aninstruction booklet. The system may be portable and thus may betransported in and out of the operating room. The system may be selfstanding and thus does not require to be hand held by a physician, nurseor a technician. In some embodiments, the system further comprises afluorescent dye.

The imaging head 230 may be comprised of a sensor, e.g., a camera 100.The imaging head 230 may, in some embodiment, also contain the energysource 130, e.g. the laser. In some embodiments the laser containedwithin the imaging head 230 provides a nominal ocular hazard distance(NOHD) of about 27 cm. The NOHD is the distance at which the beamirradiance or radiant exposure equals the corneal maximum permissibleexposure. In certain embodiments the imaging head 230 is joined to thehousing by virtue of the articulating arm.

The articulated arm provides six degrees of freedom for the imaging head230. The imaging head 230 can be translated and positioned in threelinear movements (X, Y and Z), and three angular movements (pitch, yawand roll). Pitch is the rotation of the imaging head 230 about the Yaxis. Roll is the rotation of the imaging head 230 about the X axis andYaw is the rotation of the imaging head 230 about the Z axis.

The articulated arm is comprised of three sections, the horizontalsection, the articulated section and the yoke. The horizontal sectionattaches to the cart, or housing, and provides movement along thehorizontal axis (X axis and also roll) and can move in 270 degrees offreedom. The articulated section is hinged in the middle of its lengthforming two segments. Each segment can rotate with 90 degrees of freedomin one axis. The articulated section provides movement in the verticalaxis (Z and also X and Y). The yoke section is a curved section thatattaches to the distal end of the articulated section. The yoke has tworotational attachment points. One point attaches to the articulated armand the other to the imaging head 230. The yoke provides the imaginghead 230 two rotational degrees of freedom (pitch and roll). Thearticulating arm thus provides a means for positioning the imaging head230 directly over the subject.

In certain embodiments the imaging head 230 is positioned above thepatient and the appropriate field of view is obtained with the aid ofreal time images on a computer monitor. The physician may adjust therange of focus, e.g., by intermittently observing images on the computermonitor. In another embodiment two or more laser pointers (e.g., lightsources) are provided, e.g., one at each end of the imaging head 230.These laser pointers may be the same energy source 130 as is used forexciting the fluorescent dye, or may be a different energy source 130.The laser beams may radiate green light or light at other or multiplewavelengths in the visible spectrum. The laser pointers are configuredto emit irradiation in non-parallel beams. They emanate towards thepatient or area of interest that is to be imaged. They may, for example,emanate from the imaging head.

The two laser pointers are separated by a fixed distance and angled suchthat they are in the form of two sides of a triangle. The result is thatthe two points of light will be coincident and form a single point oflight at a particular distance from the laser pointers (e.g., theapproximate distance which the imaging head must be from the area ofinterest in order to obtain a sufficiently clear image). The detectorsdetect infrared radiation in the area that is to be imaged in otherembodiments of the invention (e.g., they detect in the approximate areaof a human tissue, organ, vessel of a subject). Data obtained by thedetectors is transmitted to computer 150 having image processingsoftware. The software detects infrared radiation and thus pixelsindicative of the infrared beams have a different intensity than otherpixels. The image processing software can thus determine if there arezero, one, or two distinct dots (indicative of infrared radiation) in arow or column (or multiple rows or columns) in the imaged area.“Distinct” means that the set is surrounded by pixels that are notindicative of infrared radiation. When the imaging head is moved to ashorter distance or longer distance from the imaged area, the two pointsof light will no longer be coincident in the imaged row(s) or column(s).When the platform is moved away from the target distance the same effecthappens. The skilled artisan will understand that the beams must berelatively narrow (i.e., one beam cannot include the entire field ofview).

In one embodiment, the laser pointers are configured so that the twobeams converge at the approximate focal point of the light source usedto excite the fluorescent dye. The laser beams from the pointers pointdown toward the patient and provide a means of focusing the camera 100,without the need to look away from the patient, e.g., at a computerscreen. When the two dots from the laser beams converge the centre ofthe image is determined. The laser beams from the pointers point downtoward the patient and provide a means of focusing the camera 100,without the need to look away from the patient, e.g., at a computerscreen. If the doctor, nurse or technician determines that the beams donot converge in the approximate area where the patient is to be imaged,he can move the imaging head 230 or optics (e.g., detector(s)) with hishand until the laser pointers converge in the actual or approximate areawhere the subject will be imaged. The device may be provided withbuttons that allow for manually turning the laser pointers on and off.The buttons may be covered by the sterile drape, but may protrude enoughto facilitate ease in switching the laser pointers on and off.

In certain embodiments, I the imaging head 230 may include two lasers orlaser pointers that emit radiation in the infrared spectrum. This lasersource may emit radiation such as at 900 nm, 950 nm or some otherwavelength or combination of wavelengths. The infrared radiation isdetected by detectors described herein and detected to computer 150including image processing software. Images of the laser beam may bedisplayed visually on a display. Thus, a doctor or other attendingprofessional can determine that the energy source 130 is positioned toprovide a focused image of excited fluorescent dye without exciting thefluorescent dye (i.e. before the start of the imaging procedure).

In yet another embodiment, the infrared beams are detected by detectorsand information about them is relayed to the image processing software.The image processing software determines whether there are zero, one ortwo distinct dots or sets of pixels indicative of infrared light in theimaged area. If a determination is made that the imaging head is at anincorrect height because there is more or less than one distinct set ofpixels indicative of infrared light as imaged by the detectors, theheight of the imaging head or detectors may be adjusted throughmechanical means, such as instructions from computer 150 to a motor toturn a lead screw mechanism to obtain a linear displacement, and thusadjust the height of the imaging head or the optics (e.g., detectors),by human intervention, or by other means. The determination of whetherthe beams converge in the area to be imaged may be made once or morethan once during a procedure. For example, it may be determined onceevery 10, 20, 30, 40, 50, 60 or some other number of frames. Inembodiments where the height of the detectors or imaging head is movedwithout human intervention, the computer 150 may first instruct the heador optics be moved in one direction. The detectors then reimage the areaof interest and the data is then sent to computer 150. If the imageprocessing software determines that there are two distinct sets ofpixels indicative of infrared radiation that are further apart than inthe previous image, the computer 150 instructs the motor to move thelead screw mechanism in the opposite direction. Multiple images may beobtained at different heights of the imaging head and/or detectors untilthere is one distinct set of pixels indicative of infrared radiation inthe detected area.

FIG. 3 illustrates two light sources (e.g., laser pointers) that eachemit a beam, both beams converging at the focal distance.

In certain embodiments the computer is a personal computer 150comprising at least 512 Megabytes of random access memory (RAM) and atleast 10 Gigabytes of storage. In some embodiments the computer maycontain a Pentium IV processor (Intel, Santa Clara, Calif.). In someembodiments the computer 150 may also have a CD and DVD drive. The drivemay have read and write functionality. The system also provides imageprocessing software. The computer 150 is in electrical communicationwith the energy source 130 and detectors as described herein.

FIG. 2 illustrates a flowchart of software that may be used within thescope of the present invention. The skilled artisan will understand thatsuch software includes instructions stored on computer-readable medium.When executed, the software program provides instructions to thecomputer processor as described below. The skilled artisan will furtherunderstand that the computer is in communication with the laser, sensorand display as described herein.

At start (step 10) the user may be presented with multiple dialog boxesor other common user interface paradigms. For example, the user may bequeried about whether he wishes to start a new study (step 20). If theuser indicates that he does, he may be instructed to input or otherwiseselects a patient for the study. For example, the user may be promptedto choose a name from a list linked to a database that is accessible tothe computer. Alternately, he may be prompted to input a patientidentifier. The computer may then access the database to determine theexistence of additional information associated with the patient, andpreferably to obtain such information. In a preferred embodiment, thesoftware requires the user to input or otherwise select values forPatient First Name, Last Name and ID number fields. Most preferably,sufficient information is inputted or otherwise loaded so that imagesmay be stored according to the Digital Imaging and Communications inMedicine (DICOM) standard. The DICOM Standard is a product of the DICOMStandards Committee and its many international working groups.Day-to-day operations are managed by the National ElectricalManufacturers Association (Rosslyn, Va.). The standard is publiclyavailable at the website http://medical.nema.org/, and is incorporatedherein by reference in its entirety.

After patient data is inputted, the monitor or other display displaysimages captured by the camera or other sensor in communication with thecomputer (step 40). At this point, the user can change the position,orientation, gain or other parameter of the camera to obtain a desiredview of the patient.

Alternately, the user may choose to continue a study (step 25) at start10. Upon such indication, the process proceeds to step 40.

Once the image is displayed, the user is prompted to indicate whether hewishes to copy sequences (step 35) or acquire sequence (step 50). Theterm “sequences” refers to data associated with real-time imagescaptured by a camera or other sensor in communication with the computer.Once the user indicates that he wants to acquire images from the sensorin step 50, the computer causes the laser to turn on, and it stores thevideo sequence obtained from the sensor in RAM (step 70). Real timeimages continue to be displayed on the display. The user is then queriedabout whether he wishes to turn the laser off (step 80). If he indicatesthat he does, the computer causes the laser to shut off (step 100).Alternately, if the user does not indicate that he wants to shut off thelaser, the computer determines whether a pre-determined amount of time(e.g., 34 seconds) has elapsed from step 60. Once that pre-determinedamount of time has elapsed, the computer causes the laser to shut off.The video sequences continue to be stored in RAM until the laser isturned off. Once the laser is turned off, the user is queried as towhether he wishes to save the sequence (step 110). If he indicates inthe affirmative, then the sequences are stored to hard drive (step 120)or other media.

Returning now to step 40 for purposes of describing the software, oncethe real time image is displayed, the user is queried as to whether hewishes to copy sequences (step 35). If the user indicates that he does,the images associated with the study are selected and burned on compactdisk or other selected media (step 55). Alternately, the software mayallow the user to select specific images for storage on selected media.Preferably, the image(s) are stored in a format that is compatible witha picture archiving and computer system, for example in a DICOM format.

In another embodiment, the camera may also direct images to atelevision/VCR system such that the image(s) may be displayed in realtime and/or recorded and played back at a later time. Since the image(s)may be used to guide all or part of the surgical procedure, the image(s)may be displayed through out the length of the surgical procedure. Inother embodiments, the image(s) may be displayed for less than theentire length of the surgical procedure. In another embodiment thesoftware permits manipulating the images after acquisition, such aszooming, region of interest selection, change of brightness andcontrast, and displaying multiple images simultaneously.

In certain embodiments the image processing software permits selectionof the optimal image for analysis. In some embodiments the imageprocessing software may permit manipulation of contrast. In someembodiments the image processing software can permit manipulation ofresolution. In another embodiment the image processing software canpermit manipulation of the number of pixels in a field. In anotherembodiment the image processing software may permit control of the rateat which images are acquired. The software may be able to determine therelative contrast of one image with another, and thus select the imageshaving the greatest contrast for analysis, e.g., images of AVMs emittingdetectable fluorescence.

In certain embodiments the software may be used to compare images of preand post treatment vessels to determine flow within the vessel, e.g.,blood flow. The comparison may be performed by calculating and comparingthe area of fluorescence (e.g., the number of pixels associated with thefluorescing dye) in pre and post treatment images corresponding to aselected area of interest in the vessel. In other embodiments therelative maximum fluorescent intensity may be calculated, e.g. pre andpost-treatment. A greater number of pixels or a greater fluorescentintensity in a post treatment vessel, as compared to a pre-treatmentvessel, may be indicative of patency. Conversely, fewer (or no pixels)or less fluorescent intensity may be indicative of stenosis orocclusion.

The system also provides, in certain embodiments, for a housing tocontain the computer, the monitor, the electrical supply, the printer,and the imaging head. The housing may be portable to permit movementwithin the operating room or alternatively to permit movement of thesystem in and out of the operating room. In some embodiments the housingis comprised of at least two wheels. In other embodiments the housing iscomprised of four wheels. The wheels may have locks to prevent unwantedmovement.

In certain embodiments the housing has a width of about 30 inches, adepth of about 35 inches and height of about 82 inches. In certainembodiments the housing width is less than 40 inches. In certainembodiments the housing width is less than 45 inches. In certainembodiments the depth is less than 45 inches. In certain embodiments theheight is less than 102 inches. The housing is not hand held, and thusthe system is not required to be hand held.

The electrical power supply may be comprised of a lock in someembodiments. The lock serves as a safety device to prevent inadvertentactivation of the system, particularly activation of the laser.

In some embodiments the system may be comprised of a motion detector.The motion detector determines if the imaging head moves. In certainembodiments the system comprises a distance sensor. The distance sensordetermines the distance between the imaging head and another object,e.g. the subject. In some embodiments it incorporates a visual displaywhich provides feedback to a physician so that the laser and camera maybe located at a distance from the tissue of interest that is optimal forcapturing high quality images, thereby minimizing the need for focusingthe camera during the procedure.

The motion sensor and distance sensor may each be located on the imaginghead, for example.

In some embodiments the system comprises a sterile drape. The steriledrape covers the articulating arm to prevent or minimize the risk ofcontamination of the subject. The sterile drape may have an aperture init. The aperture may be covered with a material which is capable oftransmitting radiant energy, e.g., infra red light generated by a laser.

Apparatus

Certain embodiments of the invention provide an apparatus which may beused for intra-operative imaging e.g., in a surgical suite. Theapparatus may be portable so that it may be conveniently transportedinto and out of an operating room. The apparatus may be free standingand thus not require a physician, nurse or technician to hold it. Theapparatus may include one or more systems of the invention. In someembodiments the apparatus may also comprise at least one of thefollowing: a motion sensor; a distance sensor; a sterile drape; and aprinter. In some embodiments the housing is comprised of at least twowheels. The wheels may have locks to prevent unwanted movement. In otherembodiments the housing is comprised of four wheels. The apparatus mayalso comprise a focusing device, e.g., at least one focusing laser, e.g.a first and a second laser pointer, the first laser pointer positionedat a first end of the imaging head, and a second laser pointerpositioned at a second end of the imaging head. The two laser pointersmay be provide radiant light in the green wavelength range and mayprovide a means of focusing the camera.

The apparatus may be of a suitable size so that it is free standing, butis small enough so as not to provide a significant obstruction in anoperating room. In certain embodiments the apparatus has a width ofabout 30 inches, a depth of about 35 inches and height of about 82inches. In certain embodiments the apparatus width is less than 45inches. In certain embodiments the apparatus depth is less than 45inches. In certain embodiments the apparatus height is less than 102inches.

In yet other embodiments, the tissue of interest may be imaged with aninfrared microscope.

Example 1

This example illustrates a system of the invention. The imaging devicesis made primarily of two subsystems that are primarily optical innature, an illumination subsystem and a detection subsystem. Othersubsystems are primarily electrical or mechanical in nature. Theillumination subsystem includes a fiber-coupled, infrared laser, a lightguide, and a projector lens. The detection subsystem includes ahigh-quality imaging lens, a narrow band-pass filter, and a CCD camera.The remainder of the system includes a laser, video display, computerand other auxiliary control circuits. The system is designed with anarticulated arm with an imaging head. The imaging head contains theimaging and illumination optics and electronics. The articulated armallows the illumination and imaging systems to be positioned over thefield of operation.

Mounted inside this imaging head are the filter and CCD camera, adistance sensor and the light guide and projection lens. A powerdelivery optical fiber is routed through the articulated arm connectingthe laser to the light guide in a low-loss manner.

Illumination Subsystem

A fiber-coupled diode laser with a nominal 2 W output is used as a lightsource. Wavelength is specified to be 806 nm, which can be reachedthrough use of a thermo-electric cooler attached to the laser mechanicalpackage. For the nominally 30% efficient laser, a heat load of about 7 Wwould be offered to the surrounding mechanical structure. Thetemperature of a diode laser affects its operating wavelength, typically0.3 nm shift per degree C. Additionally, diode lasers have a maximumoperating temperature that must never be exceeded. These factors make atemperature control circuit not merely good engineering practice, butalso an environmental requirement to achieve long lifetimes (10,000+hours).

Since modern diode laser manufacturing practice cannot tightly controlthe power vs. current characteristic, each diode is different, and themaximum power for each unit will be different. The assembly andcalibration procedure will individually set the operating current foreach unit differently. Since a requirement of the system is to deliver afixed amount of power to the patient (2.0 W nominal), the illuminationsubsystem will be designed with a high enough efficiency to guarantee anexcess of power delivered when the laser is run at maximum current.During final calibration of the system, the laser diode current will bedecreased from maximum to reach the 2.0 W requirements.

The output spectrum of most diode lasers is not “line-like” as in anideal laser. The spectrum extends over several nm and usually showsprominent peaks. There is also a broad (several 10's of nm wide)low-level pedestal of power. For most fluorescence excitationapplications, the broad spectral output of these high-power laser diodesrequires an external excitation filter to prevent overlapping of thelaser light with the emission band. Prototype experiments performed haveshown that this extra filter is not required to achieve a goodsignal-to-noise ratio in the detected fluorescent image.

Power Delivery Fiber

The system uses a fiber optic cable to carry to the optical power fromthe laser diode to the optics. The laser's fiber is a multimode fiber,whose core can support many modes of laser transmission. This transferspower without burning the fiber. The core diameter (which sets theeffective emitting area) is about 200 microns. The spatial pattern oflight emitting from the fiber end is approximately a top hat (withrounded corners) in angle. The output is characterized by the fiberNumerical Aperture (NA) which is the sine of the half anglecorresponding to the HWHM. A typical power delivery fiber would have anoutput NA=0.15, corresponding to a FWHM of about 17°.

Light Guide

To project a square illumination pattern of roughly 76×76 mm the lightfrom the fiber is coupled to a light guide with a square cross section.The light guide may be made of any number of acceptable glasses (e.g.BK7). Note that some optical glasses (e.g. Pyrex) or clear plastics(e.g. polycarbonate) have a large bubble density or high refractiveindex in-homogeneity. This can lead to significant extraneous losses.The approximate dimensions are 0.25×0.25×4.00 inches. All faces shouldbe polished to approximately 50/80 scratch/dig and flat to within about5 waves. Protective chamfers (usually a good idea) are to be avoidedhere since they also can lead to significant extraneous losses.

The purpose of the light guide is to homogenize the laser light. Thecoupling from the fiber is simply an air gap of a few millimeters. Theonly requirement is that the end-face of the light guide capture all ofthe emitted cone of light from the fiber. Thus, for 0.22 NA fiber, thefiber is positioned no further away than 14 mm.

The operation of the light guide is now described. At each point on theexit face, the total laser field is the sum of several fields, some ofwhich have undergone one or more total internal reflections. Ifscattering losses are kept low, the total power reaching the exit faceequals the input power from the fiber, minus Fresnel losses at theend-faces. The radiant distribution is no longer a cone emitted from asmall fiber core, but a homogenized, square emitter, with maximum angleequal to the fiber cone angle. Homogeneity improves with length of thelight guide. Non-sequential ray-tracing calculations show uniformitywith about 20% falloff at the edges after only 4 inches of guide. Thisis not a diffuse emitter, since for each point on the end-face there arecertain definite angles of emission.

Mechanical Interface

The light guide has only a mechanical interface. Preferably, the lightguide entry face needs to be within 14 mm of the power delivery fiberexit ferrule. If the cone of light is tight enough, the groove can havea depth of 1 mm without significantly attenuating the light.

The entry face is furthermore tilted with respect to the long axis ofthe light guide. This allows mechanical access to the Fresnel-reflectedbeam. A photodiode is placed within this “stray” beam as a powermonitoring device. A tilt angle of 20° is arbitrarily chosen as acompromise. The larger the angle, the easier it is for photodiode accessand space for fiber connector. The smaller the angle, the easier tomanufacture without edge chips and the more robust the overall unit.Optically, coatings can minimize the reflection for just about anyangle, but for steep angles of incidence, there can be a greatdifference in the reflection coefficients for the two orthogonalpolarizations. It's best to keep the difference small and usenear-normal incidence angles.

Projection Lens

To project the object of square-faced emitter to the region of interestabout 30 cm away, a simple two-element air-spaced condenser lens isused. Since we want to create an illuminated region of 76.2×76.2 mm froma 6.35×6.35 mm emitter, we need a magnification of 12.0×. This definesthe ratio of image to object distance. For 320 mm (allowing somemechanical clearance for packaging), the required object distance is26.7 mm. This corresponds to using a lens with a focal length of about25 mm. The positional tolerance here is approximately ±0.5 mm.

Power Monitor

A photodiode and preamp circuit is included in the illuminationsubsystem to monitor the power being transmitted to the patient. Thephotodiode will be observing a small amount of light reflecting from theinput face of the light guide. Without an anti-reflective coating, weexpect about 4% of the total to be reflected, the usual Fresnelreflection, valid for small angles. To accommodate the reflected light,either the input face will be tilted slightly with respect to the axisof the light guide, or the fiber output will couple to the input face ata shallow angle.

The Fresnel reflections at both exit and entry faces can be eithermeasured or calculated. The transmission of the condenser lens can beeither measured or calculated. These characteristics that affect thetotal power delivered to the patient are quantities which do not changein time. It is a simple matter to generate a linear equation of powerdelivered to patient versus monitor photocurrent.

Detection Subsystem, Emission Filters

The infrared light from the laser at 806 nm excites fluorescenceindocyanine green, which has been injected into the subject'sbloodstream. The dye emits fluorescence at a peak wavelength of 830 nm.An emission filter is used to block the scattered laser light and passthe fluorescent light. Hence the filter is a bandpass filter.

The bandpass filter characteristics are a pass band centered at 830±5 nmand a 10 nm FWHM. It has a minimum attenuation in the stop band of OD 4.

The filter blocks the excitation laser light and the ambient light too.Hence, the device may be used in a brightly illuminated operating room.

Imaging Lens

The imaging lens is a commercial quality photographic lens with a maleC-mount thread for attachment to the flange on the camera. The speedshould be as fast as possible to collect the fluorescent light with thegreatest efficiency. An initial specification is one which is commonlyavailable in a variety of focal lengths—f/1.4. The CCD camera contains aCCD image sensor which is 6.45×4.84 mm (½ inch format). With a 16 mmfocal length lens (commonly available focal length), the sensor “sees” afield of 122×92 mm, just over the required 75×75 mm.

CCD Camera

The CCD camera used is a commercially available unit from Hitachi. TheKP-M2R has a spectral response that peaks at 640 nm and is useful in theNIR. Electrical power requirement is 12 VDC at 180 mA. Video output isvia RS-170 on a standard BNC mount.

Specification of Laser Class.

To determine the laser class, use 21 CFR 1040.10 as the governingdocument. We start with a nominal 3 W laser output from the square6.35×6.35 mm emitter. This radiation is inaccessible during normaloperation. It passes through a projection lens to be focused to an imageabout 300 mm away. It is accessible during normal operation immediatelyafter this lens.

The power through an aperture needs to be known to determine laserclass. This will be accomplished by estimating the radiance of the finalemitting surface (outer projection lens surface) and calculating theradiant transfer integral. The final surface of the light guide, whilenot truly diffuse, nonetheless approximates a uniformly emitting area;i.e. the power per small unit area is constant over the area of theemitter. Additionally, the emission is bounded in angle space; verylittle light is emitted at an angle greater than 8.6° (corresponding tothe input fiber NA of 0.15).

A good approximation to the radiance (power per unit area per steradian)can be calculated this way. The total power from the fiber endface is 3W. There will be approximately the same amount at the final condenserlens surface, assuming the use of good AR coatings on all surfaces. Thearea covered by the light on the final condenser surface is a square ofabout 13 mm on a side. Since the spacing from the light guide endface tothe final condenser surface is 33.6 mm, simple geometry would give 16.5mm using the 8.6° emission angle. The refraction at the first lens inthe condenser makes this a bit smaller. A ZEMAX™ ray-trace calculationwhich includes the full refractive effects of all lens surfaces yields13 mm. The emitting area is 1.69 cm². Since this lens projects an image75×75 mm at 300 mm away, the new maximum emission angle is 5.9°,corresponding to a new solid angle of 33.3×10⁻³ sr. Dividing the powerby the area and the solid angle gives L=53.3 W/cm² sr.

The radiant transfer of power Φ from a source (subscript s) to adetector (subscript d) is

$\Phi = {\int{\int{\frac{L\; \cos \; \theta_{s}\cos \; \theta_{d}}{s_{sd}^{2}}{A_{s}}{A_{d}}}}}$

where θ is the angle from the surface normal and s is the distancebetween the source and detector. The integrals are over the areas of thesource and detector. The integral can be performed under the constraintof a circular source and a circular detector, the centers of which areboth on axis. The result is

$\Phi = \frac{2\; {L\left( {\pi \; r_{s}r_{d}} \right)}^{2}}{r_{s}^{2} + r_{d}^{2} + s_{sd}^{2} + \sqrt{\left( {r_{s}^{2} + r_{d}^{2} + s_{sd}^{2}} \right)^{2} - {4r_{s}^{2}} + r_{d}^{2}}}$

In this case, the specification calls for r_(d)=0.35 cm (correspondingto a 7 mm diameter aperture) and s_(sd)=20 cm (to maintain the 10⁻³ srsolid acceptance angle). The source radius is 0.65 cm. Since s_(sd) ismuch bigger than either r_(s) or r_(d), we may approximate the result as

$\Phi = \frac{{L\left( {\pi \; r_{s}r_{d}} \right)}^{2}}{s_{sd}^{2}}$

Evaluating this expression numerically gives 68.1 mW at the detector. Abit of a subtlety in the previous calculation is that the source radiusis 0.65 cm. But the emitting area is closer to a square with side of 1.3cm. However, the approximation is good since the corners of the squareare much less bright than the center. The true illumination pattern awayfrom the exit face of the light guide is more cross-shaped than square.This laser illumination system falls well within Class IIIbspecifications.

While this invention has been described with an emphasis upon preferredembodiments, it will be obvious to those of ordinary skill in the artthat variations of the preferred embodiments may be used and that it isintended that the invention may be practiced otherwise than asspecifically described herein. Accordingly, this invention includes allmodifications encompassed within the spirit and scope of the inventionas defined by the following claims.

Many modifications and variations of this invention can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only and are not meant to be limiting in anyway. It is intended that the specification and examples be considered asexemplary only, with a true scope and spirit of the invention beingindicated by the following claims.

1. A method of intra-operatively confirming the removal of at least onevessel comprising an arteriovenous malformation in a subject comprising:a. administering a fluorescent dye to the recipient subject; b. applyinga sufficient amount of energy to the vessel such that the fluorescentdye fluoresces; c. obtaining a fluorescent image of the vessel; and d.observing the image to determine if a fluorescent signal stops at apoint of removal of the vessel, wherein a lack of a fluorescent signaldownstream of the point of removal indicates the arteriovenousmalformation has been removed.
 2. The method of claim 1, wherein therecipient subject is an animal.
 3. The method of claim 1, wherein theanimal is a human.
 4. The method of claim 1, wherein the fluorescent dyeis a tricarbocyanine dye or an analog thereof.
 5. The method of claim 1,wherein the fluorescent dye comprises a mixture or combination ofmultiple fluorescent dyes or analogs thereof.
 6. The method of claim 4,wherein the tricarbocyanine dye is indocyanine green.
 7. The method ofclaim 1, wherein the dye is administered intravenously.
 8. The method ofclaim 1, wherein the dye is administered by catheter or cannula.
 9. Themethod of claim 1, wherein the dye is administered as a bolus injection.10. The method of claim 1, wherein the dye is administered less than anhour before confirming removal of the arteriovenous malformation. 11.The method of claim 1, wherein the dye is administered more than 30seconds confirming removal of the arteriovenous malformation.
 12. Themethod of claim 1, wherein the energy is light energy.
 13. The method ofclaim 12, wherein the light energy is provided by a laser.
 14. Themethod of claim 12, wherein the light energy is provided by anincandescent light and a filter.
 15. The method of claim 12, wherein thewavelength of the light energy is in the infra-red spectrum.
 16. Themethod of claim 12, wherein the wavelength of the light energy is about805 nanometers.
 17. The method of claim 1, wherein the image is obtainedby a camera.
 18. The method of claim 17, wherein the camera is a chargecoupled device.
 19. The method of claim 17, wherein the camera is avideo recorder.
 20. The method of claim 13, wherein the laser poweroutput is about 2.5 watts.
 21. The method of claim 20, wherein the laserpower output lasts for about 30 seconds.
 22. The method of claim 20,wherein the output is a continuous wave.
 23. The method of claim 1,wherein the vessel is a blood vessel.
 24. The method of claim 1, whereinthe vessel is an artery.
 25. The method of claim 1, wherein the vesselis a vein.
 26. The method of claim 1, wherein the vessel is a nidusassociated with AVM.
 27. The method of claim 1, wherein the vessel issurgically exposed.
 28. A method of intra-operatively locating at leastone vessel comprising an arteriovenous malformation in a subjectcomprising: a. administering a fluorescent dye to the recipient subject;b. applying a sufficient amount of energy to the vessel such that thefluorescent dye fluoresces; c. obtaining a fluorescent image of thevessel; and d. observing the image to determine if the fluorescentsignal leaks from a vessel suspected of comprising an arteriovenousmalformation, wherein a leak of a fluorescent signal from a vesselsuspected of comprising an arteriovenous malformation indicates thepresence of an arteriovenous malformation.
 29. The method of claim 28,wherein the recipient subject is an animal.
 30. The method of claim 29,wherein the animal is a human.
 31. The method of claim 28, wherein thefluorescent dye is a tricarbocyanine dye or an analog thereof.
 32. Themethod of claim 31, wherein the fluorescent dye comprises a mixture orcombination of a first fluorescent dye or analogs thereof and a secondfluorescent dye or analog thereof.
 33. The method of claim 31, whereinthe tricarbocyanine dye is indocyanine green.
 34. The method of claim28, wherein the dye is administered intravenously.
 35. The method ofclaim 28, wherein the dye is administered as a bolus injection.
 36. Themethod of claim 28, wherein the dye is administered by catheter orannula.
 37. The method of claim 28, wherein the dye is administered lessthan an hour before confirming removal of the arteriovenousmalformation.
 38. The method of claim 28, wherein the dye isadministered more than 30 seconds confirming removal of thearteriovenous malformation.
 39. The method of claim 28, wherein theenergy is light energy.
 40. The method of claim 39, wherein the lightenergy is provided by a laser.
 41. The method of claim 39, wherein thelight energy is provided by an incandescent light and a filter.
 42. Themethod of claim 39, wherein the wavelength of the light energy is in theinfra-red spectrum.
 43. The method of claim 39, wherein the wavelengthof the light energy is about 805 nanometers.
 44. The method of claim 28,wherein the image is obtained by a camera.
 45. The method of claim 44,wherein the camera is a charge coupled device.
 46. The method of claim44, wherein the camera is a video recorder.
 47. The method of claim 40,wherein the laser power output is about 2.5 watts.
 48. The method ofclaim 40, wherein the laser power output lasts for about 30 seconds. 49.The method of claim 47, wherein output is a continuous wave.
 50. Themethod of claim 28, wherein the vessel is a blood vessel.
 51. The methodof claim 28, wherein the vessel is an artery.
 52. The method of claim28, wherein the vessel is a vein.
 53. The method of claim 28, whereinthe vessel is a nidus associated with AVM.
 54. The method of claim 28,wherein the vessel is surgically exposed.
 55. A portable system usefulfor imaging at least one vessel comprising an arteriovenous malformationcomprising a fluorescent dye in a subject comprising a) an energy sourcecapable of emitting sufficient energy such that the fluorescent dyefluoresces; and b) an imaging head.
 56. The system of claim 55,comprising a field of view having a first dimension of about 0.5 to 1.5inches and a second dimension of about 0.5 to about 1.5 inches.
 57. Thesystem of claim 55, wherein the first and second dimension areapproximately 1 inch.
 58. The system of claim 55, wherein the system hasan irradiance in the range of about 15-25 mW/cm².
 59. The system ofclaim 55, further comprising a means for emitting two laser beams thatare configured to converge at the approximate focal point of the energysource capable of emitting sufficient energy such that the fluorescentdye fluoresces.
 61. The system of claim 55, wherein the energy sourcethat is capable of emitting sufficient energy such that the fluorescentdye fluoresces emits the two laser beams.
 62. The system of claim 62,wherein the two laser beams comprise green light.
 63. The system ofclaim 62, wherein the two laser beams comprise radiation in the infraredspectrum.
 64. The system of claim 55, said system comprising a secondenergy source capable of emitting sufficient energy to excite a secondfluorescent dye such that said second fluorescent dye fluoresces. 65.The system of claim 55, wherein the imaging head is contained in anendoscope.
 66. The system of claim 55, wherein the imaging head iscontained in a surgical microscope.
 67. A method of imaging a vessel,comprising: a. administering a fluorescent dye to the recipient subject;b. applying a sufficient amount of energy to the vessel such that thefluorescent dye fluoresces; c. obtaining a fluorescent image of thevessel; and d. determining the presence or absence of an occlusion orstenosis, wherein jagged edges, or a change in thickness indicates astenosis and a discontinuous signal indicates an occlusion.
 68. Themethod of claim 67, wherein the recipient subject is an animal.
 69. Themethod of claim 67, wherein the animal is a human.
 70. The method ofclaim 67, wherein the fluorescent dye is a tricarbocyanine dye or ananalog thereof.
 71. The method of claim 67, wherein the fluorescent dyecomprises a mixture or combination of multiple fluorescent dyes oranalogs thereof.
 72. The method of claim 67, wherein the tricarbocyaninedye is indocyanine green.
 73. The method of claim 67, wherein the dye isadministered intravenously.
 74. The method of claim 67, wherein the dyeis administered by catheter.
 75. The method of claim 67, wherein thevessel is surgically exposed.